An elevator system has a plurality of components, such as, for example, a drive, guide rails, car guide shoes, braking systems, or similar, which must be maintained at regular intervals in order to ensure trouble-free and reliable operation. Many of these components are arranged in a shaft of the elevator system. For the maintenance tasks a maintenance engineer must be able to obtain appropriate access to the interior of the shaft. As a general rule, this takes place by way of a maintenance opening that is covered by a safety cover, such as, for example, a safety door or a panel. Since an elevator car travels in the shaft interior, special safety measures are necessary when accessing the shaft interior.
US 2004/173415 A1 describes a controllable cover for a floor door lock of a shaft door of an elevator system. In normal operation of the elevator system the cover prevents access to the floor door lock. Access is allowed if a so-called car column, or a so-called counterweight column, is set in position, and as a result the elevator car or the counterweight is unable to travel down to the floor of the shaft. In addition, in the event of a fire or another emergency, access to the floor door lock is allowed independently of the position of the car and counterweight columns. Thus only one condition must be fulfilled in order to allow access.
A locking mechanism for a shaft door of an elevator system is described in GB 1 498 039 A. The locking mechanism is deactivated if two switches arranged in series are closed. The first switch can be closed by a fitter by means of a button. The second switch is closed if an elevator car is located at a defined position. Further conditions do not need to be fulfilled in order for the locking mechanism to be deactivated.
The patent document WO 2011/076531 A1 describes a shaft access system, which is intended to ensure safe access to the shaft. The shaft access system comprises a control unit, which controls the access to the shaft, in particular by way of a shaft door. Here the shaft access system can be operated in various modes, in particular in a normal operation mode and in a maintenance mode. The mode can only be changed by an authorized person such as a maintenance engineer, by inputting a code to the control unit. With a change of operating mode one or a plurality of shaft doors are released for opening.
One disadvantage of this solution is that a change of mode can take place as a result of a software error in the control unit, or as a result of an unauthorized manipulation of the control unit. In the event of such an unauthorized change of mode the shaft doors are nevertheless released for opening. Accordingly, unauthorized persons can gain access to the shaft.
Moreover, the shaft door released for opening cannot always be arranged in the immediate vicinity of the control unit. Should for example, access to the shaft pit be enabled by way of the lowermost shaft door, and if the control unit is arranged in the region of the elevator control system in the uppermost floor of the building, then the lowermost shaft door released for opening is unsupervised for the time taken to move between the control unit and this lowermost floor door. For this time, therefore, an unauthorized person could obtain access to the shaft by way of this floor door.
For unauthorized persons without any special knowledge of the mode of operation of an elevator system, time spent in the shaft can lead to serious injury.